Irradiated proteins

Glycine, methionine, glycylglycine, and glycylmethionine solutions were selected for study primarily on the basis of electron spin resonance studies of irradiated proteins (16, 22,23,43), peptides (6), and amino acids (25) which show ... 

The data support evidence from electron spin resonance studies by Henriksen 22,23,24,25) and Gordy 16) showing that the radicals present in irradiated proteins at —80° to — 196°C. are different from those found on room temperature irradiation. They found that the free radicals produced at — 196°C. are relatively stable at that temperature, but on warming to room temperature these free radicals both react with each other and... 

Cie la, K., Roos, Y., Gluszewski, W. 2000. Denaturation process in gamma irradiated proteins studied by differential scanning calorimetry. Radiat Phys Chem 58 233-243. 

Patten F, Gordy W. Temperature effects on free radical formation and electron migration in irradiated proteins. Proc. Natl. Acad. Sci. U.S.A. 1960 46 1137-1144. 

Evidence for the activity of some radioprotectors as inhibitors of free radical processes has appeared, and the subject has been reviewed Involvement of MEA as well as of metal ionsf in free radical formation in proteins and bacteria has been observed. It was also found that cysteine and glutathione could accept electrons from irradiated proteins, whereas cystine and non-sulfur compounds did not Presence of metal ions, particularly cupric, had a protective effect for ribo-nuclease, presumably by intercepting electrons and preventing radical formation on the enzymer A protective effect of mucopolysaccharide polyanions and cysteine for trypsin and RHA, however, was not considered to be due to transfer of radiation energy to the protectors " Furthermore, substances known to react with H atoms or the aqueous electron did not protect hydrated E. coll cells from X-rays ... 

The course of chemical reactions in irradiated proteins is determined hy factors that influence the reactivity of the primary free radicals, the kind of protein radicals formed, and the decay of these protein radicals to stable products. To understand these reactions, basic radiation chemical concepts are considered, chemical changes in several representative proteins irradiated under different conditions are compared, and results from optical and electron spin resonance studies on model systems are presented. Among the reactions described are those involving cation, anion, and a-carbon radicals of amino acids and peptides. Analogous reactions common to proteins are then summarized. These mechanistic considerations have important implications for the irradiation of hydrated muscle proteins at — 40°C and for radiation sterilization of foods. 

Many of the reactions that occur in the specific systems described are common to most irradiated proteins. These reactions are summarized in the generalized scheme given below. No attempt is made to show all possible pathways for reaction or to explain all of the observations noted for proteins. For the sake of clarity, the protein structure is idealized and schematically represented by /X/X/X/X/X/, which is equivalent to (20) (details in the structure are included only for specific cases) ... 

Miller et al. (135) reported on distribution of free radicals among amino acids from lyophilized UV-irradiated proteins. 

Tritiated Free Radical Scavengers in the Study of the Irradiated Protein Molecule... 

Strong evidence has been presented (JO, 13, 18) that the sulfur pattern in the ESR spectra of irradiated proteins is caused by the —CH2—S- radicals formed from cystme. However, when ribonuclease is irradiated to 34 Mrads in the absence of air and subsequently dissolved in water, definitive chemical experiments (28) show no appreciable breaking of disulfide bridges. Possibly these apparently conflicting results might be reconciled by supposing that broken disulfide bridges (one per molecule) may rejoin in aqueous solution,... 

Under irradiation, proteins are affected by direct and indirect effects of ionizing radiations. When these macromolecules are in liquid solution, direct effects can be neglected and the indirect effects are predominant. On the contrary, in solid state, proteins are ionized mainly by direct interaction (11). 

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